During maneuvers for parking a vehicle, it is not possible to perceive exactly the distance between the vehicle and the obstacles that lie in the parking area, particularly during reversing maneuvers or maneuvers for approach on the opposite side with respect to the driver. Moreover, it is not infrequent to find oneself in a condition in which some obstacles are completely concealed and invisible to the driver, as occurs in the case of obstacles located in corners that are covered by the vehicle structure itself or are very low, for example the typical bollards used to delimit parking areas, or simple poles.
In order to solve the drawback and thus avoid unpleasant accidents, systems are known which are provided with sensors for detecting the distance between the motor vehicle and the surrounding obstacles.
Systems using ultrasonic sensors are mainly used for measuring the distance between an obstacle and a motor vehicle; these sensors detect a signal emitted previously by a radiating element located in the vicinity of the sensor and reflected by an obstacle that lies proximate to the vehicle.
During an adequate time window, the received return signal, known as echo signal, is compared with a threshold value, and if said threshold value is exceeded, the sensor generates a warning signal.
In these systems, it is particularly important to avoid the emission of incorrect warning signals and to increase the precision of the assisted parking system. Incorrect warning signals refer in particular to signals reflected by objects that do not constitute a danger of collision with the vehicle, such as for example the ground, the optional towing hook mounted on the vehicle, particularly distant obstacles, or signals caused by noise.
For this purpose, currently it is known to adjust the time window so as to exclude from the comparison with the threshold values the signals caused by particularly distant obstacles. The duration of the time window in fact determines the monitoring depth of the system.
As an alternative, it is common to vary the duration of the signals emitted by the radiating element of the sensor or to vary the power radiated by said signals.
Finally, it is also known to act on the threshold values, which can vary according to time. Generally, the threshold values are reduced monotonically over time until the end of the time window, in order to prevent the system from generating warning signals caused by extremely proximate signals produced by the reflection of the ultrasound for example against the ground or against the towing hook.
Other known systems adapt the threshold values to the physical parameters of the car in order to further increase the precision of the system. Moreover, these threshold values are changed dynamically also according to the direction of travel of the vehicle, so as to increase the sensitivity of the sensors located in the direction of travel and reduce the sensitivity of the remaining ones.
The need to detect the various obstacles that are present around the vehicle and to take into account the various factors described above in order to provide the driver with the most precise possible information causes sensing systems to be complicated and scarcely flexible. In particular, one of the problems that most significantly affect the manufacture of sensors is the need to calibrate correctly the sensor depending on the position where it will have to be installed on the motor vehicle, requiring a specific programming of the control unit and a different configuration of the sensors provided in the sensing system.
Further, sensing devices according to the background art, while having a plurality of sensors capable of ensuring a good vision of the surrounding area, do not allow to use the sensors selectively: the signals returned by each sensor remain within a sequential reading cycle even when some of them are not useful or relevant during a specific maneuver or travel condition.